In the 90s as a student I had a friend, who was manager of the local cinema. I was often visiting there behind the scene and occasionally helped carrying those 5000ft (IIRC) reels to the projectors. Anyway, once he took me to another older cinema. They still had a lot of the old equipment there, including a projector with the old electric arc lamp, using a carbon anode that had to be continuously adjusted for the length loss through burn. Manually of course. It also had a read head for 'magnetic sound'. Prints with magnetic sound hadn't been made for a long time then. Too expensive, but higher fidelity than the optical version. So my friend was hoping to 'inherit' that beast from the boss. So about burning rolls of film. There was an old solid wooden storage cabinet. Each film roll (probably 1000ft?) would go into its own slot with lid. The wood was probably treated and the whole thing made sure that a fire wouldn't ignite any rolls in storage. So you'd never have 1000m of film in one place. While I mentioned the modern 5000ft rell back then they didn't glue (can't be bothered to find the right term, right now) together the individual rolls but used two projectors to run them sequentially and fade over. And if the operator didn't pay attention the screen would go white! The projected film was running through a kind of fire trap (probably two metal plates sandwiching the film, or similar). So if the film were to be ignited by the heat of the lamp, because of an accidental stoppage, the combustion would stop right there. Just cut the burned section, glue the ends together and continue.